An organic light-emitting diode (OLED) is a light-emitting device in which the emissive layer is a film of organic compound which emits light in response to an electric current. This layer of organic semiconductor is located between two electrodes. Generally, at least one of these electrodes is transparent.
OLEDs have been employed to produce digital displays in devices such as television screens, computer monitors, portable devices such as mobile phones, handheld game consoles and personal digital assistants (PDAs). Besides, a major area of research is the development of white OLED devices for use in solid-state lighting applications.
Generally, an OILED has high internal quantum efficiency. However, a large amount of light emitted from the emissive layer is confined inside the OLED. This is because a large amount of light is confined inside organic materials and a transparent substrate, which causes the external quantum efficiency of the OLED is about 20%. As a result, how to increase the external quantum efficiency is important for the development of the OLED.